28 TIMBER AND TIMBER TREES. 



which the burning properties of wood are due. These 

 organic and readily combustible constituents of timber 

 affect its durability in many ways ; not only are they 

 apt to oxidise in the air, but it is these bodies which 

 are consumed by various insects and fungi and other 

 organisms which destroy the timber. 



Clearly, therefore, the points of view from which 

 the forest botanist examines and reports upon our piece 

 of wood, affect the arts in very many ways. Not only 

 so. The discovery that wood is a complex structure 

 of tubular elements, the walls of which are capable o 

 absorbing or giving off water, entirely modifies all the 

 older views as to the " porosity " of timber. We must 

 not compare a piece of wood to a piece of chalk, or 

 brick, or other capillary absorbent; the water which 

 passes into the tubes (vessels, tracheids, cells, etc.) 

 must be distinguished carefully from the water absorbed, 

 and held much faster, in the porous walls of these 

 elements. And similarly with regard to air. This not, 

 only concerns all views as to the physical properties of 

 wood, but it shows that any mere weighing of equal 

 volumes of two different timbers by no means gives 

 accurate results as to their specific gravities, for in- 

 stance. You might as well take two chambered boxes 

 of equal size, filled with different substances, and imagine 

 that their comparative weights gave you a constant of 

 value, as compare directly the weights of a cubic foot 

 of two different kinds of timber without regard to their 

 structure and other peculiarities. 



Moreover, the study of timber from these points of 

 view profoundly affects all experiments on its infiltration 

 or impregnation with various poisonous preservative sub- 

 stances. The difficulty of forcing solutions of phenol, 

 cupric sulphate, mercury salts, etc., into wood, by the 



